In the empty Replayer app, you can either use ready-made compilations, or you can load individual tracks in one of the supported audio format to create your own compilation. Click the Click / drop to load file(s) button to use the "Open files..." dialog or just drag and drop media files onto the button control.
Image: Adding media files to an empty compilation
Replayer automatically opens the edit mode, and creates a track for each file. The track name is derived from the file name.
Image: Generated Tracks from opened files. The plus sign allows to add more
At any time, in the edit mode, you can add more files to a compilation by clicking the plus sign below, and repeating the step above.
Now you can start to edit the track.